It is well known in the art that the mineralization of dental deposits and the subsequent formation of calculus (hydroxyapatite deposit) occurs via a homogenous nucleation (an increase in Ca.sup.++ ions or orthophosphate ions) and/or via heterogeneous nucleation (specific salivary and bacterial proteins). However, in either case, salivary Ca.sup.+2 is added to the salivary orthophosphate leading to hydroxyapatite (HAP) formation. The formation of HAP in vitro occurs in two distinct steps:
1. When Ca.sup.+2 is added to orthophosphate at constant pH (7.4, by pH stat), there is rapid consumption of base as a function of time, that is, 1-4 minutes. PA1 2. Then the base consumption diminishes for about 15-20 minutes after which the second uptake of base occurs. A delay in the time of the second rapid consumption of base, or a total absence of a second rapid consumption suggests an interference with the crystal growth of HAP. Accordingly, compounds which interfere with crystal growth of HAP are effective anti-calculus agents. PA1 1. a copolymer of maleic acid or anhydride and of an olefin having 2 or more carbon atoms per molecule, PA1 2. sulfoacrylic oligomers having an average molecular weight of less than 1000, and PA1 3. a tricarboxy-oxa-butanol or pentanol, and is ionically bound to a dissociable, physiologically acceptable magnesium compound.
It is also known that the magnesium ion, Mg.sup.+2, reduces the overall rate of crystallization by stabilizing the precursor (amorphous deposit) formed initially with Ca.sup.+2 and orthophosphate, as disclosed in "Growth of Calcium Phosphates on Hydroxyapatite Crystals: The Effect of Magnesium", Arch. Oral Biol, 20:803, 1975. The amorphous deposits are readily removable while the crystalline phase is difficult to remove. However, the residence time of externally introduced Mg.sup.+2 ion in the oral cavity is low. Saliva also has an extremely low Mg.sup.+2 content (J. Periodontal Res. 9:211-221, 1974).
It has now been found that the efficacy of the magnesium ions can be improved by combining magnesium with a polycarboxylate selected from the group consisting of the maleic acid copolymers, the sulfoacrylic oligomers and the tricarboxy-oxa-butanol or pentanol to form a complex therewith. Since there are at least two carboxyl groups per mole of polycarboxyl-containing compound (e.g. two carboxyl groups per mole of maleic acid), one carboxyl is available to react with Mg.sup.+2 (2/3 ionized) and there are enough free COO.sup.- to react with the tooth enamel.